Radio receivers, or tuners, are widely used in applications requiring the reception of electromagnetic energy. Applications can include broadcast receivers such as radio and television, set top boxes for cable television, cable modems, receivers in local area networks, test and measurement equipment, radar receivers, air traffic control receivers, and microwave communication links among others. Transmission of the electromagnetic energy may be over a transmission line or by electromagnetic waves.
Many applications require a receiver that can tune to multiple channels at the same time. For example, Picture in Picture (PiP) is a feature that is enabled by some television receivers and set top boxes. The PiP feature allows for one program to be fully displayed on a television screen, while one or more additional programs are displayed in inset windows at the same time.
Similarly, the Data Over Cable System Interface Specification (DOCSIS) 3.0 requires compliant cable modem receivers to have the ability to tune to multiple downstream channels at the same time. The term DOCSIS generally refers to a group of specifications published by CableLabs that define industry standards for cable headend and cable modem equipment. In part, DOCSIS sets forth requirements and objectives for various aspects of cable modem systems including operations support systems, management, data interfaces, as well as network layer, data link layer, and physical layer transport for data over cable systems. The most current version of the DOCSIS specification is DOCSIS 3.0.
In order to stay competitive with providers offering telecommunications services over fiber, and to better support bandwidth intensive applications, such as video-over-IP, DOCSIS 3.0 provides for a new feature referred to as channel bonding. This new feature calls for the bonding of any four channels in a contiguous 64 MHz bandwidth centered anywhere between 54 MHz and 1 GHz. In downstream transmissions, from a cable headend to a cable modem located at a subscriber premise, each downstream channel occupies a separate 6 MHz or 8 MHz frequency band and is capable of carrying a payload of approximately 38 Mbps (50 Mbps in Euro DOCSIS compliant systems). Channel bonding allows for a load to be distributed among multiple RF channels, allowing for a maximum throughput of n*38 Mbps (with n being the number of bonded channels).
Traditional cable modem receivers utilize a dual-conversion tuner architecture that is capable of down-converting a single channel. This dual conversion architecture typically utilizes two complex mixers and a surface acoustic wave (SAW) filter. The SAW filter is a mechanically resonant device that is typically fabricated on a ceramic substrate, and therefore cannot be integrated on-chip with the other tuner components. As such, the SAW filter remains a discrete component in many tuner designs, preventing the tuners from being fabricated on a single silicon substrate.
A simple approach to comply with the channel bonding standard specified in DOCSIS 3.0 is to use four instances of the traditional single channel tuner. Although this implementation can provide for the greatest flexibility in selecting multiple, non-contiguous channels in the downstream bandwidth, this solution requires a high component count, including four separate SAW filters, and a large amount of area in an IC implementation.
Alternatively, a single tuner architecture can be used that can down-convert four or more RF channels within any 64 MHz bandwidth. A single tuner architecture can provide for reductions in power consumption and silicon area. However, conventional implementations of this architecture typically require a SAW filter, as well as a large analog-to-digital converter (ADC) capable of handling bandwidths up to and in excess of 64 MHz.
Therefore, what is needed is new receiver and tuner architectures that provide flexibility in the selection and down-conversion of multiple RF channels, while at the same time eliminating the need for expensive, area-consuming components, such as SAW filters and high-bandwidth ADCs.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.